Learning and generalization in healthy aging: implication for frontostriatal and hippocampal function.

Damage to the hippocampal and frontostriatal systems can occur across the adult life span. As these 2 systems are involved in learning processes, mild impairments of learning and generalization might be observed even in healthy aging. In this study, we examined both learning and generalization performance in 3 groups of older adults: young-older (ages 45 to 60 y), middle-older (ages 61 to 75 y), and oldest-older (ages 76 to 90 y).

Neuronal localization of cholecystokinin mRNA in the rat brain by using in situ hybridization histochemistry.

The distribution of cholecystokinin (CCK) mRNA in the rat brain was determined by means of in situ hybridization histochemistry. Our results demonstrate a widespread distribution of neurons containing CCK mRNA throughout the rat brain. Hybridization-positive neurons were distributed throughout the neocortex, olfactory bulb, claustrum, amygdala, the dentate gyrus and hippocampus proper, and several subnuclei of the thalamus and the hypothalamus.

Neonatal sensory deprivation reduces tufted cell number in mouse olfactory bulbs.

Quantitative morphometric methods were used in mice to study the effect postnatal olfactory deprivation has on tufted cell size and number. The two layers containing tufted cells, the external plexiform and glomerular layers, are considerably smaller in the deprived olfactory bulbs than in the contralateral, experienced olfactory bulbs. While most of this volumetric deficit may be due to an attenuation of synaptogenesis and dendritic elaboration, an additional factor contributing to the reduced volume of these bulbar layers is a substantial loss of tufted cells.

Effects of early anosmia on two classes of granule cells in developing mouse olfactory bulbs.

Quantitative morphometric methods were used to examine the effects of early unilateral anosmia on two classes of granule cells in developing mouse olfactory bulbs. Volumetric results show that the internal granule cell layer in the deprived olfactory bulb is significantly smaller than the same layer in the experienced olfactory bulb. The major factor contributing to this retarded development is a selective loss of one class of interneurons; dark granule cell number is substantially reduced, while light granule cell number is not.